Masters Degrees (Soil, Crop and Climate Sciences)
Permanent URI for this collection
Browse
Browsing Masters Degrees (Soil, Crop and Climate Sciences) by Author "Bennie, A. T. P."
Now showing 1 - 5 of 5
Results Per Page
Sort Options
Item Open Access Besproeibaarheid van gestruktureerde gronde(University of the Free State, 1991-11) Nell, Johannes Petrus; Bennie, A. T. P.Afrikaans: Data van 333 profiele se fisiese (breukmodulus, infiltrasie, hidrouliese geleivermoë, lugwaterdeurlatendheidverhouding, waterretensie en Atterberggrense), chemiese (KUK, UNP, NAV, pH, elektriese weerstand, elektriese geleivermoë, Fe-SBD, Al-SBD en organiese koolstof) , morfologiese (grondkleur, struktuur, kleiverhoudings en slik tot kleiverhoudings) en kleimineralogiese eienskappe was gebruik om neokutanies, pedokutanies, prismakutanies, rooi gestruktuurde en vertiese gronde te karakteriseer. Gronde van 15 dreineringstreke is in die ondersoek gebruik. Klem word egter op kalkryke gronde in die Sondagsrivier-, Klein-Visrivier- en Groot-Visrivierdreinerings- gebied geplaas, aangesien heelwat van die gronde deur verdere ontwikkeling van die Oranjerivierprojek geraak word. Daar bestaan regverdiging om verskille tussen diagnostiese horisonte as besproeiingsnorm te gebruik, aangesien duidelike fisiese en chemiese verskille tussen grondvorms, binne dreineringsgebiede voorkom. Daar is 'n afname in die geskiktheid van gronde vir besproeiing met 'n toename in graad van struktuurontwikkeling. Dit kan hoofsaaklik toegeskryf word aan 'n toename in opbou van skadelike soute en 'n verskuiwing van 'n oorwegend illietiese kleimineraalsamestelling na 'n smektietiese samestelling wat tot swelling en/of dispersie aanleiding gee. Laer infiltrasie en hidrouliese geleivermoë waardes, met 'n toename in struktuurontwikkeling, kan grootliks hieraan gewei word. Alhoewel die Na-inhoud ook 'n rol speel by die strukturele eienskappe van vertiese en rooi gestruktuurde gronde, het die tipe en hoeveelheid kleiminerale en seskwioksiedes 'n duideliker invloed by dié gronde se struktuurstabiliteit. Daar bestaan egter nie regverdiging om kleur volgens seriedifferensiasie as besproeiingsnorm by pedokutaniese gronde te gebruik nie. Die stabiliserende effek van die ysteroksiedes wat vir rooi grondkleur verantwoordelik is, word egter in sommige dreinerings- gebiede oorbeklemtoon. Die soort en hoeveelheid soute tesame met die tipe kleiminerale het 'n meer dominante invloed op hierdie gronde se struktuurstabiliteit. Die groot variasie in hidrouliese eienskappe van gestruktuurde gronde kan moontlik beter verstaan word, indien die beskrywing van die graad, tipe en grootte van die struktuureenhede met spesifieke parameters gekwantifiseer kan word. Die oorgang tussen horisonte is ook van belang. By dupleksgronde kom daar in die algemeen 'n drastiese afname in infiltrasie van die A- na die B-horisonte voor. Die lae infiltrasievermoë van die B- horisonte veroorsaak dat horisontale infiltrasie tot 'n groter mate as vertikale infiltrasie plaasvind. Aansienlike interkorrelasie tussen fisiese, chemiese en kleimineralogiese eienskappe kom voor wat tot lae verwantskappe aanleiding gee. Indien gronde egter in pedologiese eenhede gegroepeer word en die korrelasies vergelyk word, kan sommige daarvan verhoog of beter verstaan word.Item Open Access The compaction susceptibility of soils in the Free State(University of the Free State, 1998-12) Nhantumbo, Alfredo Bernardino Julio Da Costa; Bennie, A. T. P.Crop production in the Free State is mainly performed on sandy soils. The compaction of these apedal soils can present a management problem which affects crop yields and financial returns. In addition, environmental problems such as soil erosion and siltation of rivers may result. The main objective of the study was to see whether the easily measured soil properties, texture and organic matter, could be used to classify the compact ion degree of soils and to predict their compaction susceptibility. Additional objectives were to define critical densities beyond which crop growth would be impeded, to test the applicability of the relative bulk density concept proposed by Bennie & Van Antwerpen (1988) and to propose a procedure for the prediction and classification of the compactibility of the soils in the Free State. Finally, the results were compared to the data from forestry soils (Smith, 1995) for more humid conditions. Twenty two (22) samples of selected soils covering a large range of soil texture variation were submitted to a determination of the maximum bulk density (using the Proctor test), minimum bulk density, uniaxial compression test and penetrometer resistance measurements. A procedure for the determination of minimum bulk density was developed. Good quadratic relationships were obtained between the maximum bulk density and silt plus clay or organic matter content as loss on ignition. The minimum bulk density can be predicted from the silt plus clay percentage or loss on ignition. When the actual bulk density and the silt plus clay or loss on ignition percentages are available, the relationships allow the estimation of maximum and minimum bulk densities. The measured bulk density can then be used to calculate the relative bulk density of a soil. Threshold relative bulk density classes (5) were derived which can be used to evaluate the degree of denseness or looseness of the soil, and its suitability for different applications. It is proposed that compactibility be regarded as the difference between the maximum and minimum bulk densities, instead of simply the maximum bulk density. Different classes of compactibility were derived. The compression index of all the soils at the critical water content showed good relationships with the silt plus clay, clay or organic matter contents of the soils. Compressibility classes were also established. A combination of the compactibility and compressibility of soils was used to determine its susceptibility to compaction. Compaction susceptibility was classified into five groups varying from very low to very high degrees of susceptibility for apedal soils. The data set from this study when combined with the data reported from the study of forestry soils by Smith (1995), made it possible to derive equations with a more universal applicability for the prediction of the maximum and minimum bulk densities, critical water content as well as compression index. The results from this investigation, when properly transferred in popular terminology set guidelines for the evaluation of the degree of compactness and compaction susceptibility of soils. These guidelines will allow persons responsible for soil evaluation to draw more meaningful conclusions from bulk density measurements.Item Open Access The effect of crop residue cover and soil texture on crusting(University of the Free State, 2002-10) Massingue, Felicidade Isabel; Bennie, A. T. P.Large areas of cultivated soils throughout the world develop rainfall-induced soil crusts. The soil crusts are usually the cause of reduced seedling emergence. To have quantitative information on the factors influencing the development of surface crusts and on the influence of ameliorating treatments on crust strength is valuable. The objectives of this study were firstly, to determine the influence of soil texture on the susceptibility of different soils for crusting; secondly, to quantify the effect of soil crusts on the emergence of wheat, sorghum, soybean and sunflower; and thirdly to determine the optimum level of crop residues that can be used as a mulch to mitigate the effect of soil crust strength. Five soils ranging in texture from sand to loam were sampled from the surface (0 - 200 mm). The soil samples were used in four greenhouse pot experiments that were conducted to examine the effect of crust strength on seedling emergence. Separate pot experiments in the greenhouse were conducted to determine how particle size distribution was related to soil crust strength. Regression analyses showed that silt, silt plus clay and clay contents were related to crust strength as indicated by modulus of rupture, penetration resistance and emergence force. All the relationships were of third order polynomial nature. The crust strength increased initially with increasing silt plus clay contents up to about 35 to 40 %, or clay contents up to about 25 %, then declined as a result of cracking that occurred upon drying. The emergence of wheat, soybean and sunflower was little affected at crust strengths less than 0.7 Mpa or 500 gf when measured as penetration resistance and emergence force respectively. Above these values seedling emergence decreased linearly with increasing crust strength. Large areas of cultivated soils throughout the world develop rainfall-induced soil crusts. The soil crusts are usually the cause of reduced seedling emergence. To have quantitative information on the factors influencing the development of surface crusts and on the influence of ameliorating treatments on crust strength is valuable. The objectives of this study were firstly, to determine the influence of soil texture on the susceptibility of different soils for crusting; secondly, to quantify the effect of soil crusts on the emergence of wheat, sorghum, soybean and sunflower; and thirdly to determine the optimum level of crop residues that can be used as a mulch to mitigate the effect of soil crust strength. Five soils ranging in texture from sand to loam were sampled from the surface (0 - 200 mm). The soil samples were used in four greenhouse pot experiments that were conducted to examine the effect of crust strength on seedling emergence. Separate pot experiments in the greenhouse were conducted to determine how particle size distribution was related to soil crust strength. Regression analyses showed that silt, silt plus clay and clay contents were related to crust strength as indicated by modulus of rupture, penetration resistance and emergence force. All the relationships were of third order polynomial nature. The crust strength increased initially with increasing silt plus clay contents up to about 35 to 40 %, or clay contents up to about 25 %, then declined as a result of cracking that occurred upon drying. The emergence of wheat, soybean and sunflower was little affected at crust strengths less than 0.7 Mpa or 500 gf when measured as penetration resistance and emergence force respectively. Above these values seedling emergence decreased linearly with increasing crust strength.Item Open Access A laboratory characterization of the upward flux of nitrate from a shallow water table in a sandy loam soil(University of the Free State, 2002-12) Weldeyohannes, Amanuel Oqbit; Bennie, A. T. P.Shallow water tables are common in areas that have been irrigated for several decades and are reported to be one of the causes for increased salinity in large irrigation fields. Upward flux of solutes from a shallow water table can occur as a result of evaporation and plant water uptake. Evaporation-driven fluxes will have positive and negative implications on agricultural production. Thus, characterization of the upward flux of solutes in soils is important for the accurate prediction of arrival times and spatial patterns of solutes coming from shallow water tables. The main objectives of the study were as follows. Firstly to become acquainted with tracing techniques used to quantify water and solute upward fluxes. Secondly to quantify the effect of time, flux rate, and solute concentration on the upward movement of nitrate ions. Thirdly to evaluate prediction procedures for nitrate movement and/or hydraulic properties for the sandy loam soil. Three laboratory experiments on repacked homogeneous sandy loam subsoil columns were conducted with water tables maintained at a depth of 750 mm and using nitrate as an anion tracer. These were, varying time with a constant groundwater N03--concentration and flux rate, varying flux rate at a constant time and groundwater N03--concentration and finally varying groundwater N03--concentration at a constant time and flux rate. The upward mass flow of N03- was measured and calculated by the mass flow component of the convective-dispersion equation (eDE). Results of N03-- concentration and water content showed temporal and spatial variation in all the experiments that agreed with the theoretical approaches found in literature. In all three experiments the theoretically calculated and actual measured N03-- accumulations in the soil column were compared. The theoretically calculated values were higher than the measured. Denitrification losses during the experiments were put forward as the reason for the lower measured N03--concentration. The measured upward mass flow N03--accumulation increased as a function of time, flux rate and N03--concentration level in the groundwater solution with the highest accumulation in the top surface layer. The hydraulic soil properties were determined and fitted to the two-part retentivity function of Hutson & Cass. The hydraulic conductivity vs matric potential and hydraulic diffusivity vs water content relationships were also derived for the experimental soil. It was concluded that higher N03--concentrations in the groundwater, than the 25 mg N03- r' used in this study, should be used in future studies and a concentration of 100 mg N03- 1-1was recommended. The 20 day durations of the experiments were also too short because it allowed for only about 0.6 to 0.8 pore volumes of cumulative flux at rates of 6 to 8 mm d", This was insufficient to reach equilibrium conditions. Longer experiments of up to 60 days were recommended.Item Open Access Leaching of excess salts from the root zone of apedal soils(University of the Free State, 2006-05) Barnard, Johannes Hendrikus; Van Rensburg, L. D.; Bennie, A. T. P.English: In South Africa a huge amount of energy was spend on irrigation research over the past two decades, mainly to optimise water application in order to prevent crop water stress. In the quest to conserve water for transpiration, researchers tended to neglect the importance of drainage or percolation, which eventually results in the accumulation of salts in the root zone. Salts also accumulate in the root zone where shallow water tables are present. Farmers along the Lower Vaal River expressed their concern about yield losses induced by build-up of salts in the root zone. The detrimental affect of salinity on field crops are extensively reported in the literature and the only way to address the problem is through leaching. Sustainable utilization of these saline or potential saline soils depends on adequate natural drainage or artificial drainage systems, which ensures a net downward flux of water and salts below the root zone for optimum development and functioning of roots. This dissertation focuses mainly on the management of salts in the root zone of apedal soils. The research was conducted on two soil types (Clovelly and Bainsvlei) reconstructed in 5000 litre lysimeters on the experimental farm, near Bloemfontein, of the Department of Soil, Crop and Climate Sciences (University of the Free State). A total of 30 lysimeters, 15 per soil type arranged in two parallel rows under a moveable rain shelter were used. It was assumed that the artificially prepared soil profiles are stable because more than 10 cropping cycles were completed before the commencement of this experiment. The first aim of Chapter 3 was to address the effect of irrigation water salinity on the accumulation of salt in the root zone under shallow water table conditions. A total of 612 mm was irrigated with irrigation water salinity treatments that varied between 15 and 600 mS m-1. Results showed that in the absence of drainage, salts will accumulate in the root zone at an alarming rate. In fact, salinity of the soil water almost doubled with respect to that of the irrigation water during only one growing season. These various saline profiles were used to characterise the impact of soil water salinity on the hydraulic characteristics of the two soils under investigation. After saturation of the profiles, drainage curves were in situ determined by allowing water to drain freely from the profiles for approximately a month. These drainage curves revealed that the initial soil water salinity did not significantly influence the hydraulic characteristics of both soils. It was possible to quantify the amount of salt removed during a drainage cycle. Although both soils are apedal, the two soils differed markedly in their discharge rates and amounts. Chapter 4 had focused on quantifying the pore volume of water required to leach excess salts from the profiles. It was found that piston flow can describe the leaching process, because one pore volume of drainage was sufficient to remove 100% of the excess salts, irrespective irrigation water salinity or soil water salinity. The results also showed that it is more efficient to remove 80% of excess salts in stead of 100%. On freely drained soils it is therefore possible to effectively and efficiently manage the salinity level of the root zone through controlled irrigation in excess of crop water demand, when necessary. Complex dynamic models are helpful in understanding the nature and complexity of solute movement in soils, but unfortunately they are not widely used by irrigators and managers. The final objective (Chapter 5) was to derive a simple model capable of estimating the depth of water required to remove excess salts from the root zone. The non-linear exponential association (y = a {1- exp –b x}) of the in situ determined leaching curves provided the best mathematical description of the fraction of excess salts removed in relation to the depth of leaching water required per unit depth of soil. Verification of the proposed model showed that it is possible to accurately estimate the leaching requirement for effective and efficient management of root zone salinity in apedal soils. It was recommended that the proposed model should be expanded to include more soil types.